run.py: Make Xen treat OSv image as QCOW2 file

Xen requires explicit image format specification.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
build: option to choose OSv image format via make command line

Default image format stays QCOW2 as before.  May be changed via img_format
variable:

  make img_fomat=raw all

This option is required by release-ec2 script as EC2 does not support QCOW2.
Also will be useful for other hypervisors like VMWARE.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
release-ec2: force build to create raw OSv image

EC2 does not support QCOW2. Force build to create RAW image.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>